1. Field of the Invention
The present invention relates to an embedment-type semiconductor laser having both side surfaces of a ridge embedded in a current blocking layer and method for manufacturing the same
2. Background Art
Embedment-type semiconductor lasers having both side surfaces of a ridge embedded in a current blocking layer are being widely used (see, for example, Japanese Patent Laid-Open No. 3-97290). FIG. 5 is a sectional view of a conventional semiconductor laser. A ridge 5 having an active layer 2 and a p-type InP clad layer 3 and an n-type InP clad layer 4 disposed on opposite sides of the active layer 2 is provided on a p-type InP substrate 1. Two side surfaces of the ridge 5 are embedded in a current blocking layer 6. An n-type InP contact layer 7 is provided on the ridge 5 and the current blocking layer 6. The current blocking layer 6 includes a p-type InP layer 8, an n-type InP layer 9 and a p-type InP layer 10 stacked in order from the p-type InP substrate 1 side.
A distance L is the shortest distance between the n-type InP layer 9 in the current blocking layer 6 and the n-type InP contact layer 7. The distance L is determined by the layer thickness of the p-type InP layer 10. The distance L first determined and the distance L after the completion of the wafer process are substantially equal to each other. If the distance L is small, electrons in the n-type InP contact layer 7 can overflow into the p-type InP layer 10 and flow into the n-type InP layer 9. Since these electrons are not injected into the active layer 2, they flow as a leak current, so that the optical output is reduced. When the semiconductor laser is operated by causing a large current to flow therethrough, the overflow of electrons is increased. In such a case, therefore, the problem becomes more serious.
FIG. 6 is a diagram showing current-optical output characteristics of the conventional semiconductor laser. A simulation was made by maintaining the ambient temperature at 95 degrees C. with respect to different values of the distance L of 100 nm, 250 nm, and 300 nm. The results of this simulation show that the optical output is reduced when the distance L is smaller than 300 nm.